1. Field of the Invention
The present invention relates to a method for web tension adjustment in a processing machine, to a processing machine, to a corresponding computer program, and to a corresponding computer program product.
Although reference will made hereinafter primarily to printing presses, the invention is not limited to them, but instead is directed to all types of processing machines in which a web of goods or web of material is processed. The invention is especially usable, however, in printing presses, such as newspaper printing presses, job printing presses, intaglio presses, inline flexographic printing presses, packaging printing presses, or securities printing presses as well as in processing machines such as bag-making machines, envelope-making machines, or packaging machines. The web of goods may be of paper, fabric, cardboard, plastic, metal, rubber, or in the form of foil or film, and so forth.
2. Description of the Prior Art
In processing machines, especially printing presses, a web of goods is moved along by driven shafts (web transport shafts), such as tension rollers or feed rollers, and nondriven shafts, such as deflection rollers, control rollers, and drying or cooling rollers. Simultaneously, by means of usually driven processing shafts, the web of goods is processed, for instance being imprinted, stamped, cut, folded, and so forth.
The web tension of the web of goods is varied for instance via so-called clamping points, which clamp the web of goods by positive or nonpositive engagement. Typically, this involves transporting or processing mechanisms that are driven. In an intaglio press, a clamping point is typically formed by a printing unit, in which a frictional-engagement unit is between the driven impression cylinder, the presser, and the web of material. The web of goods is subdivided into web tension segments, and one web tension segment is defined by two clamping points. Within one web tension segment, further driven and/or nondriven shafts may be disposed. Often, the entire web of goods is subdivided into a plurality of web tension segments, including those with different set-point web tension values. For maintaining the set-point values, a web tension controller is typically employed.
The adjustment or regulation of the web tension of a web tension segment can be done by various methods. The word “downstream” means that the clamping point that defines the web tension segment downstream is adjusted, while “upstream” means that the clamping point defining the web tension segment upstream is adjusted. However, in this simple embodiment, the web tension in subsequent web tension segments is not decoupled from the control motion. Instead, the change in web tension along the course of the web of goods is transported through the machine and has to be compensated for in all the subsequent segments.
In downstream regulation by means of a (dynamic) downstream pilot control, it is possible to pilot-control all the slave clamping points such that they directly compensate for the effects of the master clamping point. It is consequently ensured that all the following web tension controllers need not compensate for the disruptions of coupling by the web of material.
In German Patent Disclosure DE 10 2008 056 132, which was not published prior to the filing date of the present application, decoupling for an upstream controller is proposed, in which in addition to a (constant) upstream pilot control, a (dynamic) downstream pilot control is also performed by means of a PT1 element.
All the known decoupling strategies have the disadvantage that slave clamping points have to be pilot-controlled. If now for mechanical, structural or other kinds of prerequisites (such as a constant delivery speed) it is impossible to include the slave clamping points in the closed-loop control circuit, then in both regulating strategies the pilot controls required for the decoupling cannot be employed. Moreover, especially in large systems, it is undesirable, after an adjustment at a master clamping point, to adjust all the slave clamping points as well.